Magnesium alloy for die casting

ABSTRACT

A die cast alloy of magnesium has been produced which contains the following ingredients:   ALL OF THE PERCENTAGES EXPRESSED ON A WEIGHT BASIS. This alloy has good castability properties coupled with reduced creep extension.

United States Patent Foerster et a1. July 1, 1975 MAGNESIUM ALLOY FOR DIE CASTING 393,837 6/1933 United Kingdom 75/168 D 51 ,4 4 K' d H 7' [75] Inventors: George S. Foerster, Monmouth 6 64 Ummd mg om 3/168 C Junction; Charles D. Statham, Trenton, both of NJ. Primary ExaminerC. Lovell [73] Assignee: N L Industries, Incorporated, New

57 ABSTRACT 22 F1 d: O t. 1 1973 1 c A die cast alloy of magnesium has been produced 1 1 pp 402,019 which contains the following ingredients:

[52] US. Cl .1 75/168 C; 75/168 B; 75/168 D;

148/32 5.0% to 200% zinc 0% 815% l 511 lm. Cl. C22c 23/00 ;3 60% g 'gg [58] Field of Search 75/168 B, 168 C, 168 D, 10(5):: :0 rnlenganesc O SI ICOn 75/168 M, 168 E, 168 F, 148/32, 164/284, 303 he remainder magnesium [56] References Cited UNITED STATES PATENTS all of the percentages expressed on a weight basis. 1,341,774 6/1920 Backer 75/168 C Thi h d Stability properties coupled with FOREIGN PATENTS OR APPLICATIONS reduced Creep exlension 382,420 10/1931 United Kingdom 75/168 C 2 Claims Drawing Figure E a .E E a I: a-

D 1 c O 5 l0 15 2O 7,, Zinc 1 MAGNESIUM ALLOY FOR DIE CASTING BACKGROUND OF THE INVENTION Various magnesium base alloys are described in the art which are useful for die casting. Most of these alloys contain relatively large amounts of aluminum and small amounts of zinc. The instant invention is particularly concerned with the alloys which contain relatively large amounts of zinc and small amounts of aluminum. Although the prior art has prepared alloys containing aluminum and zinc, the prior art has failed to teach the preparation of alloys which have the combination of good castability with a decrease in creep extension.

SUMMARY OF THE INVENTION A ductile die cast alloy of magnesium has been prepared comprising aluminum, zinc, copper and manganese with the optional addition of silicon, the balance being magnesium, said alloy having an aluminum and zinc composition by weight which falls within the composition range represented by the pentagon shaped area A, B, C, D and E and bounded by the straight lines AB, BC, CD DE and EA of the graph in the appended drawing, and containing in addition from 0.6 percent to 6.0 percent copper and from 0.05 percent to 3.0 percent manganese, the balance magnesium.

Compositions of aluminum and zonc represented by the area covered by the pentagon ABCDE correspond in general to the range of zinc in the alloy from 5.0 percent to 20.0 percent and aluminum from percent to 8.5 percent. The alloys also contain copper in amount from 0.6 percent to 6.0 percent, manganese in amount from 0.05 percent to 3.0 percent, the balance being magnesium all of the percentages expressed on a weight basis.

The pentagon is bounded by straight lines connecting the following points:

Zn Al A 5.0 8.5 B [0.0 8.5 C 20.0 0.0 D [0.0 0.0 E 5.0 4.0

DESCRIPTION OF THE DRAWING Magnesium based alloys containing zinc and aluminum which fall within the compositions contemplated by the instant invention are shown in the drawing. The drawing represents the diagram of the composition Zn Al defined by the pentagon ABCDE which is bound by the lines AB, BC, CD, DE and EA.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 5 kilo pounds per square inch (k.s.i.) for l00 hours at 350F. The addition of silicon up to 2.0 percent also tends to improve the fluidity and strength.

Alloys which are prepared having zinc contents below the minimum amount specified above have poor castability while alloys prepared having zinc contents above the maximum amounts specified become brittle.

It has also been found that the maximum amount of copper employed preferrably should be no more than 0.5 times the zinc content.

In order to describe the instant invention in more detail, the following examples are presented:

EXAMPLES 1-7 Several magnesium base alloys containing various amounts of zinc, aluminum, manganese and copper were prepared. All of these alloys fell within the zinc and aluminum pentagon ABCDE.

The compositions of the various alloys are recorded in Table l.

The various alloys were produced by melting commercial grade magnesium at l300F under halide flux cover. Zinc, aluminum and copper chunks in the desired proportions as shown in the Table were added to the molten magnesium to dissolve the chunks. The manganese was added as manganese chloride. The soprepared melts were then each die cast into a heated die at 500F and 8,000 psi, having a cavity configuration of an ASTM E8-68, FIG. le, 2 inch gauge length test bar. These bars were then tested for yield strength ultimate tensile strength, and percent creep at a tensile loading of 5 k.s.i. for I00 hours at 350F. All data are recorded in the table.

For comparative purposes, alloys having compositions which contain less than 0.6 percent copper but which lie inside the pentagon ABCDE were prepared as controls and their results were compared with the above examples.

These compositions and their properties are also recorded in the table as Controls A-D.

It has also been discovered that the presence of manganese in amounts from 0.05 percent to 3.0 percent is effective in increasing the corrosion resistance and tends to improve the creep resistance.

The corrosion resistance of these alloys was deter mined as follows:

Standard die-cast tensile bars were cut in half to ob tain corrosion test specimens 4 /2 inches long with a major diameter of inch. After cleaning to remove surface contamination, the specimens were weighed and then partially submerged in aerated 3% NaCl solution saturated with MgO (pl-I 10.3) for three days at room temperature. The specimens were mounted vertically through holes in a plastic sheet which served as the cover of the test vessel. Approximately of the specimen length was submerged. At the end of the test period, the products were removed by immersing the specimens in a solution containing 20% CrO and l% AgNO The final weights were then determined and the average corrosion rates calculated from weight loss, submerged area, and test duration.

It should be noted that the creep extensions of Examples l-6 were all less than all of the corresponding controls which contained less than 0.6 percent copper. In addition to improved creep resistance, these alloys also possess satisfactory corrosion resistance. From the above examples, it has clearly been shown that alloys ing of zinc, aluminum, copper, manganese, silicon and magnesium, said zinc and aluminum present in amounts which fall within the pentagon ABCDE in the accompaning drawing defined by the lines AB, BC, CD, DE and EA, said alloy also containing copper in amount from 0.6 percent to 6.0 percent, manganese in amount from 0.05 percent to 3.0 percent, silicon in amount from 0.0 percent to 2.0 percent, the remainder magnesium, all of the percentages expressed on a weight basis.

2. A die cast alloy of magnesium according to claim TABLE COMPOSITION AS CAST (Room Temperature) Ultimate Yield Tensile Corrosion Strength Strength Creep Resistance %Al %An %Cu %Mn Ksi Control A 0.0 15.9 0.3 2.! 26.5 33.2 3.0 4.84 0.7 Example l 0.0 l5!) 1.] 2.l 27.9 37.4 4.5 3.l 69 Example 2 0.0 15.) 3.2 2.| 26.8 34.3 4.0 l.2l 096 Control B 4.2 12.2 0.35 0.3 28.1 37.5 3.9 .62 0.l7 Example 3 4.2 12.2 l.l 0.3 28.2 35.7 2.6 .36 026 Example 4 4.2 12.2 3.l 0.3 29.6 37.0 2.0 .32 0.36 Control C 7.1 6.6 0 .2] 25.2 34.2 2.6 2.47 Example 5 7.l 6.6 L0 .2l 27.8 37.) 42 L48 0.22 Example 6 7.l 6.6 3.2 .2] 29.2 37.4 2.1 0.50 0.52 %Si Control D 3.8 9.6 0 .l4 1.0 25.6 34.] 2.8 0.90 Example 7' 3.8 9.6 0.95 .14 l.0 27.3 36.6 3.8 0.24 0.20

We claim: 1 in which the copper content of said alloy should be no more than 0.5 times the zinc content. 

1. A DIE CAST ALLOY OF MAGNESIUM HAVING GOOD CASTABILITY AND IMPROVED CREEP EXTENSION, SAID ALLOY CONSISTING OF ZINC, ALUMINUM, COPPER, MANGANESE, SILICON AND MAGNESIUM, SAID ZINC AND ALUMINUM PRESENT IN AMOUNTS WHICH FALL WITHIN THE PENTAGON ABCDE IN THE ACCOMPANING DRAWING DEFINED BY THE LINES AB, BC, CD, DE AND EA, SAID ALLOY ALSO CONTAINING COPPER IN AMOUNT FROM 0.6 PERCENT TO 6.0 PERCENT, MANGANESE IN AMOUNT FROM 0.05 PERCENT TO 3.0 PERCENT, SILICON IN AMOUNT FROM 0.0 PERCENT TO 2.0 PERCENT, THE REMAINDER MAGNESIUM, ALL OF THE PERCENTAGES EXPRESSED ON A WEIGHT BASIS.
 2. A die cast alloy of magnesium according to claim 1 in which the copper content of said alloy should be no more than 0.5 times the zinc content. 